A US woman who shot and killed her husband and two adult children before taking her own life is thought to have committed the shocking crime as a result of being ostracised from the religion she was raised in.

Every time I tell a mate I’m doing a story on cryptocurrency, they invariably ask me the same two questions: should they invest their own hard-earned money, and which cryptocurrency will get them a Lamborghini/yacht/island quickest?

WA surfer critical after shark takes leg 'from the knee down'

A 29-year-old surfer is fighting for his life in a Perth hospital after a shark bit off most of his leg at a beach in Mandurah.

Ben Gerring was among 20 surfers were enjoying a large swell at Gearies near the suburb of Flacon around 4pm yesterday when "all hell broke loose".

"He was right out the back looking to get a big wave, one of the set waves that had been coming through during the day," one of Mr Gerring's mates, Brian Williams, told the ABC.

"He'd sort of paddled out the back, sort of past the pack slightly. And next thing all hell broke loose and they were trying to bring him in. His board was broken in half, they found the tail part of his board."

Halls Head resident Jodie Hough told PerthNow that Mr Gerring appeared to still be conscious when he was dragged out of the surf, but that his leg below the right knee was gone.

Nathan Hondros, a reporter with the Mandurah Mail, told the national broadcaster the immediate aftermath of the attack was harrowing to watch.

"Ambulance crews were trying to resuscitate him by the looks of it," he said.